Textile carding systems generally include a fiber feeding device, such as a chute feed, which accumulates a quantity of fiber and forms such fiber into a batt that is delivered to a card which separates the fibers into their individual elements, cleans the fiber, and forms the fiber into a sliver for use in the next step in the textile processing of the fiber. The card includes three basic components, namely an input feed roller which receives the aforesaid batt, a main carding cylinder which works the fiber, and a doffer which removes the fiber from the main cylinder and delivers the fiber through a trumpet or the like in sliver form. Traditionally, the doffer and the input feed roller were driven together through a mechanical driver arrangement that assured a constant speed ratio between the input feed roller and the doffer.
However, in an effort to improve sliver uniformity and reduce yarn count variation caused by insufficient control of the batt delivered to the card, autoleveling has largely replaced the aforesaid traditional direct, mechanical drive between the doffer and the input feed roller. Autoleveling may take a variety of forms, but it typically includes a variable speed transmission, such as an electrical drive system which results in the doffer and the input feed roller being driven at a predetermined speed ratio, and which also permits this ratio to be varied in response to variations in the density of the sliver leaving the doffer so as to provide a more uniform sliver.
The advantages of autoleveling are well known in the trade insofar as improved sliver characteristics are concerned, but known autoleveling systems nevertheless have some recognized disadvantages. For example, in autoleveling systems which sense the density of the sliver leaving the trumpet and then adjusts the speed of the input feed roll, it is apparent that the compensating effect caused by adjusting the input feed roll is imposed at one end of the card in response to a sensed density variation occurring at the other end of the card. As a result, the correcting speed change imposed on the input feed roll will have no compensating effect on the substantial length (e.g. 100 yards) of fiber which is being processed between the ends thereof by the main cylinder so that density variations in this intermediate length of fiber will not be corrected before such fiber leaves the card. Likewise, because the density sensing occurs at a location substantially downstream of the point where the compensating speed change is made, it may well be that the density variation at the sensing location will have already been partially or fully corrected in the fiber at the input feed roll when that portion of the sensed fiber reaches the trumpet so that the compensating speed change may cause an undesirable change in the density of the fiber rather than a correcting change.
Additionally, most conventional autoleveler equipment utilizes an air stream to sense the density of the sliver, but the fineness of the fiber in the sliver may cause variation in the air flow therethrough which are not directly attributable to fiber density, and this flow variation may adversely affect the accuracy of the sensing apparatus which, in turn, may adversely affect the compensating speed change imposed on the input feed roll of the card. Moreover, the use of air has inherent drawbacks, such as dirt entrained in the air stream and the fact that the humidity of the air may affect the accuracy of the density sensing apparatus, and it is therefore usually necessary to provide relatively expensive equipment to insure that the air is dry and clean as well as to provide relatively frequent maintenance for such equipment.
Another known method of autoleveling is described in Krull U.S. Pat. No. 4,206,823 and provides an arrangement for feeding the batt through a pair of compressor rolls as it leaves the fiber feeding apparatus and then weighing the batt by a sensitive load beam transducer that provides a signal which is processed through a central processing unit to regulate the speed of the feed rolls of the card and the compressor rolls. However, the speed change imposed on the feed rolls of the card also changes the proportional speed relatively between the doffer roll of the card and the feed rolls, whereby there may be an undesirable and adverse effect on the parallelization and drafting of the fiber during the carding of such fiber.
Finally, it is also known that more effective control of the batt leaving the fiber feeding apparatus may be obtained by controlling the operation of the opening roller in the fiber feeding apparatus in response to the level of the fiber accumulated in the fiber feeding apparatus. The opening roller is directly driven by a motor, and an electric eye is used to sense the level of the accumulated fiber and generate a signal which is applied to either vary the speed of or start and stop, the opening roller motor whereby more or less fiber is fed into the fiber feeding apparatus. In apparatus of this type, the opening roller motor is operated entirely independently of the card, and variations in the card speed (e.g. slow speed during start up, or the on-off condition of the card) may not reflect in the operation of the opening roll of the fiber feeding apparatus so that the density of the batt leaving the fiber feeding apparatus may not be attuned to the operation of the card to which the batt is delivered.